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Dr. E. Hull. Note on Dr. Hinde s Paper [Apr. 28, 



April 28, 1887. 



Professor STOKES, D.C.L., President, in the Chair. 



The Presents received were laid on the table, and thanks ordered 

 for them. 



The following Papers were read : — 



I. "Note on Dr. G. J. Hinde's Paper 'On Beds of Sponge- 

 remains in the Lower and Upper Greeosand of the South 

 of England' ('Philosophical Transactions,' 1885, p. 403):' 

 By Edward Hull, LL.D., F.R.S., &c, Director of the 

 Geological Survey of Ireland. Received March 17, 1887. 



In a valuable communication read before the Society in May, 1885, 

 Dr. Hinde has given an account of the bands of siliceous material, 

 generally in the form of " chert," found at intervals in the two Green- 

 sand formations of the Cretaceous period throughout the south of 

 England — clearly indicating the extent to which siliceous sponges 

 contributed to the formation of the successive sea-beds of this period ; 

 an extent to which, as the " Challenger " soundings show, has its 

 parallel in some parts of the ocean at the present day. 



In discussing the origin of the chert and chalcedonic bands in 

 which the spicules are imbedded, or out of which they have been dis- 

 solved, leaving cavities in their place, Dr. Hinde states his opinion that 

 " There can scarcely be room for doubting that the beds and irregular 

 masses of chert . . . have been derived from the silica of these 

 sponge-remains; and from the same source has also originated the 

 silica* which, in many of the deposits — more particularly in the 

 Blackdown Hills — has replaced the shells and tests of the mollusca 

 and other calcareous organisms." He proceeds to say, " The theory 

 has, however, been advocated that the silica of the chert has been 

 derived rather as a direct deposit of this mineral from solution in sea- 

 water, than as the product of the decomposition of the siliceous struc- 

 ture of the sponges. Thus Dr. Bowerbank held that the sponges 

 imbedded in the chert of the Greensand possessed horny and not 

 siliceous skeletons, and that the silica in the chert in which they were 

 imbedded was attracted from the exterior medium by the animal 

 matter, and not secreted from the living sponge. Professor T. 

 Rupert Jones maintains the view that the silica of the chert is derived 



* The italics are not in the original. 



